The present invention relates to an end fitting for realizing joints for wooden beams as well as a method for realizing such joints.
More particularly the invention concerns a metal end fitting or member for realizing truss joints of wooden beams adapted to build tridimensional trusses, and a method for accomplishing such joints.
When building tridimensional truss structures for roofing various kind of buildings such as gyms, conference rooms, show-rooms, swimming pools, etc., there are generally employed steel beams joined together by weldings formed in the field during the structure assembly.
Further to such kind of buildings, more recently there has been a spreading of wood use in form of laminar wood beams, for the roofing of both areas and buildings having an architectural relevance, where a particular importance is attached to the aesthetic appearance or harmony.
A problem in building wooden truss structures resides in the difficulty of firmly joining the beams to each other by using connectors allowing the proper orientation of the beams.
In the years several solutions have been suggested to solve the problem of forming joints among wooden beams that are adapted to build tridimensional truss structures.
In accordance with a first solution, metal plates are secured by pins or screws to the beam end for the connection of the beam to another one.
According to this solution the beam is thus clamped between two metal plates.
An alternative solution provides for inserting the plates into slots milled at the ends of the beams and fastening them by means of steel bolts.
Relying on this system in 1988 the roofing of the Oguni gym on mount Aso in Japan was built.
According to a second solution, metal tubular end members are inserted into longitudinal holes drilled at the ends of the beams.
Such metal tubular end members are further provided at the end protruding from the beam, with means adapted to allow the joining of a beam to another either directly or through a polygonal member called core fitting, adapted to receive a plurality of such end fittings.
These metal tubular end fittings are generally secured to the wooden beams through a plurality of radial pins crossing the beam sides and the tubular end fitting.
A drawback when using the above illustrated methods providing for pins or bolts comes from the weakening of the fibrous structure of the wood beam caused by the presence of the steel bolts or the radial pins since the beams are cut so as to have the wood natural fibers parallel to the beam longitudinal axis to take advantage of the beam resistance to traction and bending.
When the structure is subjected to stresses, the transversely extending bolts fastening the plates tend to spread apart the wood fibers thus reducing the connection strength and therefore requiring the use of large size bolts and beams that raises the weight and the costs of the structure.
A not negligible drawback of these known methods derives from their long execution times because radial holes are to be drilled and suitable pins, or bolts are to be properly positioned to realize the joint between the beams.
Several methods have been suggested to build trusses that overcome these drawbacks.
One of such methods is disclosed in EP-A-0 651 099. According to the teaching of this European Patent Application a joint for connecting together beams for building tridimensional truss structures comprises a core fitting provided with a plurality of metal tubes each preset to be inserted and stuck to a hole drilled at the ends of each wooden beam.
The metal tube is glued to the beam by injecting a resin into a channel provided in the tube, after the tube has been inserted into the hole drilled at the beam end.
The injected resin issues from the tube end that is inserted in the beam and fills the gap or clearance existing between the hole and the metal tube, and leaks outside the hole housing the metal tube.
Although this method does not require a fastening through bolts, thus avoiding the drawbacks of the prior art, it has other drawbacks that render its accomplishment quite difficult.
A drawback of the system disclosed. in EP-A-0 651 099 is due to the fact that the glueing between the metal tubes and the wooden beams must preferably be carried out after the structure has already been assembled.
Since the resin has to be injected after the structure has been assembled, the workers have to operate under unfavorable circumstances with the structure being subjected to forces and movements that reduce the glueing efficiency.
Moreover, in order to carry out the glueing operation the diameter of the hole drilled in the beam must be slightly larger that that of the metal tube, so that a sufficient amount of resin can be spread between the metal tube and the beam. For this reason during the assembling of the structure slight relative movements can occur between the metal tube and the beam and such movements can endanger a correct glueing.
A further drawback of the system described in the above patent application derives from the fact that a large amount of resin is wasted to fill the injection channel provided inside the tube.
Therefore the tube to be inserted into the beam must be equipped with a small-size resin injecting channel which in turn will increase the mass of the tube that will be substantially solid and provided with a thin injection channel.
A first object of the present invention is to provide an end fitting for realizing joints for wooden beams that is devoid of the drawbacks of the above illustrated prior art.
This object of the present invention is accomplished through an end fitting for wooden beams as claimed in claims from 1 to 6.
A second object of the present invention is to provide a method for realizing joints in wooden beams quickly and at low cost.
This object of the present invention is accomplished through a method for realizing joints in wooden beams as claimed in claims 7 to 9.
The end fitting of the present invention comprises a tubular member to be inserted into a longitudinal hole drilled at the end of a beam made of laminar wood.
Advantageously such end fitting comprises a tranverse plate provided with means for centering and blocking the fitting while the resin solidifies.
The tubular member is further provided with an outer surface. that is threaded, embossed or machined so as to increase the surface in contact with the resin.
The joint for connecting together two or more beams is obtained by glueing the body of the end fitting into the beam hole that has been filled in advance with a proper amount of resin.
After curing, the resin encircles the end fitting body for its whole length that has been inserted into the beam and transfer the forces generated at the structure panel points parallely to the wood fibers, thus increasing the joint strength.
Additional characteristics and advantages of the invention will become evident from the following description of a preferred and not-exclusive embodiment thereof illustrated in the attached drawings in which: